Laminated spring.



n. LANDAU.

LAMINATED SPRING.

APPucmon FILED Auelzz. Isls.

1,241,743. Pand ont. 2,1917.

i @nvm/Q01 `D.'LANDAU.

- LAMINATED sPmNG. APPLICATIUK FILED AUG. 221 |916.

1,241,743. mm o@ 2,1917.

z ,sains-skater 2.

FIGS

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FIGS

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LAMINATED SPRING.

Specification of Letters Patent.

Patented Oct. 2.V 1917.

Application Med Aug-ust 22, 1916. Serial N o. 116,284.

To all whom z't may concern:

Be it known that I, DAVID LANDAU, a

citizen of the United States, residin'g inL fork,`

the city, county, end State of-New have invented certain new and useful Improvements in Laminated Springs, of which the following is a specification.

This invention relates to laminated springs, such as are used for the suspension of vehicles, and, more particularly, to supporting springs for vehicles designed to meet the requireriients of particular classes of service, which will be referred tomore in detail hereafter.

In my PatentNo. 1,199,013', dated September 19th, 1916, I have disclosed and fully explained certain basic improvements in spring construction of my invention having general applicability to laminated springs, and the' present yinvention' makes use of certain of these improved features, and also.

additional fedtures of improvement in meeting particular conditions which are frequertly found in practice. '"As to certain principles enunciated in my former patent, the present invention constitutes a particular application to meet the special conditions to be dealt with.

The primary object of all vehicle springs is to act as a cushion, that is, to inter-pose a yielding resistance to sudden movements which absorb the shock and decreases the subjected were those resulting from direct vertical loads producing bending stresses,

then certain conditions would govern the spring design, which, however, do not always obtain in practice. Thus the springs, in Yaddition to serving as cushions, also commonly serve as the means for connecting the vehicle to the running Igear. The springs are, therefore, subjected to longitudinal, lateral and torsional stresses. As a -particular and notable example of this, the rear springs of many motor-driven vehicles may be noted; for instance, in the case Vof vehicles having what is known as the Hotchkiss drive in which, as is well known, the reaction from the drivingr wheels is transmitted to the vehicle entirely through the springs. Under such circumstances, the rear springs, and more particularly the master leaves thereof by which the springs are actually connected' to the vehicle body, act

as struts or tie rods and are subjected to4 severe' stresses differing in kind and dei gree from the stresses which the spring is compelled to withstand when it acts merely as a cushion to take up vertical' shocks. Leaf springs and particularly the master leaves thereof are also subjected to other kinds of stresses due to lateralv sway of vehicles to which they are attached, and particularly when there is a depression of the springs at one side of the Vehicle body more than on the other side. In the last-named case torsional stresses are set up in the 'master leaves of the springs and to a lesser degree also in the other leaves.

` The eil'ects above referred to, namely, the stresses due' to the action of the springs as struts and that due to the lateral and torsional stresses referred to, are most marked in the master leaves thereof, while another effect which -also imposes severe stresses on the master leaf is that produced by the initial internal stresses set up in the springs, due to the initial curvature of the separate leaves or nip therein. It is well known to those versed in the art .that in order to,

maintain the several lea'ves of a laminated spring` in contact at all times, and to prevent chattering dueto the separation and the comin together again ,of the leaf ends, the severa leaves of a spring must be given different initial curvatures, the longer leaves being less curved and` the shorter .leaves more curved, so that when the lepves are bound together .they will maintam their' close contact. 'l`he binding together at the center of these variously curved leaves results however in producing initially in the longer and straighter leaves of thespring,

a negative stress, or stress in the opposite direction to that imposed u pon the spring.

by the external load; therefore, when the spring, as a whole, is greatly stressed, as when encounterin an obstruction, the na- Iture of the stress 1n the longer leaves may `change fxromnegative to positive, thus producing a reversal of stress, which, as is well known, imposes a much greater tax. on the powersof resistance of a piece of material t0 fatigue than mere variation in the value of the stress when always of the same character and sense.l f

As a result of the foregoing effects, it is clear that there is a tendency for the master ing leaf, and less so for the longer leaves of the spring, to be stressed more severely than the shorter leaves of the spring; and colisequently, unless steps are taken to counteract this condition, the master leaf of the spring will be the first to break, especially if the spring is subjected to extreme deflections, and will certainly `be the first to fail from continued use. As I have explained in my former patent, however, it is very undesirable that the master leaf should break first, as the failure of the master leaf which ultimately supports the load, necessarily places the spring as a whole out of use, and hence will put the vehicle out of commission until repairs can be made or a new spring secured. Moreover, the unexpected breaking of the master leaf may let the load down upon the axle with dangerous results.4 The master leaf heilig also the longest leaf of the spring and the most expensive and difficult to replace, whereas, on the other hand, if one of the shorter leaves of the spring breaks first, it does not at once put the spring out of commission, but will permit of the spring being used with ordinary care for some time or until an opportunity is alforded for mak- 4ing repairs, while the breaking of one of the shorter leaves forms an effective warnthat repairs are needed, or, that a change in the conditions under which the spring is Y being used, is required if breakage is to be avoided. It will therefore, be'seen that it is highly `desirable that the springs shall be so designed that the short leaf, or, one of the shorter leaves, shall break before the master leaf or long leaves give way.

In my patent above referred to, I have set forth the underlying principles of spring construction which I have discovered and have-therein disclosed how vehicle springs can be constructed in which the short leaves Will break before the master leaf. One of the means which I have set forth by which this result may be obtained consists in the use, of a master leaf thinner than the other leaves of the spring, or preferably, in which the leaves are inversely graded in thickness from the master leaf to the short leaf, the former being the thinnest and the latter the thickest. A spring havin this characteristic is ideally suited to con itions where it is .subjected wholly or chielly to vertical cushioning stresses, as for example, in the case 0f front springs of a motor-drlven veh1cle,

and is the most eflicient spring which can be used for that purpose;

that is to say, it will support the heaviest load and provide the greatest resistance to fatigue for a given 'weight of material embodied in its construction. ,Where the spring, however, is subjected to additional extraneous stresses, and particularly where it is called 4upon to act as a strut in transmitting the driving re.- action from the rear wheels of a motordriven vehicle, the thin master leaf may not be capable of performing satisfactorily. Under such circumstances, it is usually, if not always desirable, toemploy a thick master leaf which is generally thicker than the other leaves of the spring. Accordingly the springs of motor vehicles in which driving stresses are transmitted, are very-commonly of the type known as Lgraded springs. This type of spring is characterized by the fact that the master leaf is thicker than the other` leaves, the leaves usually being graded in thickness from the thick master leaf to a thin short leaf. Such graded springs as heretofore used, ho'wever, have been eX- tremely inefficient in that the material has been unevenly stressed, some parts of the spring doin more than their share of work, while, `in ot er and. major parts, the metal has been used nowhere near to its ultimate capacity. In order to enable the overstressed portion of the spring to stand up, a large excess 0f material has, accordingly, been required and such springs have, therefore, been unduly heavy, while at the same time, they were likely to break under conditions of any severity and subject to early fatigue failures. By the present invention, 1 provide a spring of the graded type, or one having a thick master leaf, which is thereby applicable to cases where it is required to withstand driving` stresses, or to be employed in other cases where a graded spring is desirable, such improved spring being so constructed that the short, or one of the shorter leaves, will break before the master leaf, possessing, therefore, the advantages attendant upon such quality, the spring being also characterized by a very high degree of efficiency in the quantity of material employed. whereby the spring will be relatively light in weight, an important consideration especially in motor vehicles, while still possessing great strength and durability.

In order to illustrate the nature of my invention and to explain the manner of constructing the spring, in order to secure the novel and beneficial results thereof, I will now describe in detail certain speciic'embodiments of my invention, which are shown in the drawings accompanying and forming a part of this specification. In these drawings, Figure 1 is a diagrammatic side elevation of a spring containing one such embodiment. Fig. 2 is a bottom plan view of the spring shown in Fig. l. Fig. 3 is a diagrammatic side elevation of the leaves of the spring before being bound together and showing the different free curvatures of the leaves. Fig. 4 is a diagrammatic View of the rear end of the chassis of a motor vehicle showing the rear axle connected to the frame by means of a rear spring which acts as a strut and `tie rod in transmitting the able spring seat or pero driving power fromthe wheels to the vehicle frame. Figs. 5 and 6 are views in plan and vertical section, a spring leaf showing a form of 'ta er and stress rectifyin slot which may e employed. Figs. views showing forms of de ressions which may be provided in the lealP ends to reduce the section modulus and obtain an effect similar to that produced by cutting the metal entirely through. Figs. 11 and 12 are a plan view and a vertical section, respectively, of portions of the upper leaves of a spring showing a construction for introducing lubricant between the leaves.

Referring to the drawings in detail, and particularlyto Figs. 1 to 4, it will be seen that the lower or semi-elliptic portion 1 of the sprin assembly shown in Fig. 4 and illustrate in detail in Figs. 1, 2 and 3, is a graded spring in which the master leaf 2 is the thickest, and theshort plate 3 the thinnest. The master leaf is provided at its ends with the eyes 4 which receive the shackle bolts 5 (see Fig.v fl by which the spring is connected to the ve icle frame, and to the other parts of thespring assembl if such there be, such as the quarter-elli tlc spring member 6. Below the master lea in Fig. 1 is the long -plate 7which preferabl has its ends extending under the master lea the axes of the shackle bolts.4 The ends of the long plate are' preferably not tapered at all, or, at least, but very little. Between the long plate and the short plate are a series of intermediate plates or leaves 8, the number of which will depend upon the load carried and the deflections desired and the endurance sought. The short plate 3 is su ported upon a suitli 9 on the axle, the

spring being attached to the axle in any suitable manner as by means of the usual box clips or bolts 10. In its fully-assembled condition, the several leaves of the spring are bound together at the center by suitable means, such as the center bolt 11. The master leaf may also if desired be connected at least as far as p with the long plate or plates by means of the rebound clips 12. Before the leaves are assembled, however, they are given different curvatures increasing toward the short plate so that the Afree curvatures ofthe several leaves is of the general character illustrated in Fig. 3. These curvatures and the mode of action of the leaves will be more fully described hereinafter.

It will be seen that the plates below the long plate gradually decrease in length, the steps or overhangs between the several leaves not being uniform, however, but gradually increasing from the longer to the shorter plates. Thus, it will be seen that the overhang of the short plate 3 represented by the distance a between the perch and the end respectively, of a portion of 8, 9, and 10 are lsimilar` Vmy former patent above constructions, which I ferred to.

of the plate is greater than the overhang b' of the next plate, which, in turn, is greater than the overhang b2 of the plate above it, and so on, up to the lon plate. The ends of the leaves below the ong plate are also tapered, the length or fineness of the taper increasing from the plate below the long plate to the short plate, which short plate has the longest and most flexible taper of all. Various forms of tapers may be employed, some of the' possible forms being shown in referred to and the taper may be either in thickness only, or in width only, though it is much preferable to taper in both width and thickness. As illustrated, the ends of these leaves have tapers in thickness of the character which have designated as trapezoidal in my former patent as shown in Fig. 1 and are tapered in parabolic outline in width, as appears in Fig. 2. The ta ered ends or points of the leaves below a so preferably overlap the bases of the tapers of the leaves above, particularly in the case of the shorter and more tapered leaves. As illustrated, the intermediate leaves of the sprin are also provided in the portionsl of such eaves immediately inside of the ends of the leaves below or adjacent to the bases of the tapers, with stress-rectifying slots 13 of the nature and for the purpose explained in detail in my previous patent. It will be understood Athat these slots may be ofany suitable form and may, in fact, not be actual slots, but may be perforations as indicated in my previous patent, or may be mere depressions, as illustrated in Figs. 7 to 10, inclusive, a further description of which will be given herea er.

Considering now the action of the spring having the structure 'which I have described and the underlying reasons which have led me to adopt this structure, I will refer to certain fundamental principles of spring have discovered and which are set forth in my previous patent re- As there elucidated, it appears that the eifective re-actions or mutual ressures between the adjacent leaves of a faminated spring are exerted wholly or chiefly at the extremities or ing leaves. It further appears that in a thickness and decreasin in length from the long plate to the short p ate by an arithmetical progression so as to produce equal steps or over-hangs and in which the leaves are not tapered, the supporting ability of the spring does not increase proportionately to the number of leaves, but is much less than the stren h of an individual leaf multiplied by t e number of leaves. This it was shown is due to the fact that the reactions between the leaves are not uniform but decrease toward the long plate with the result points of the support.

`spring having a number of leaves of equal that the nietal is not uniformly stressed nor efficiently used.

1 further pointed out that by tapering the ends of the leaves so that their stepped lengths or overhanging portions have the flexibility of eantaliver beams of uniform strength, the reactions can be inade equal and that by further increasing the flexibility of the tapers, the reactions can be made to increase toward the long plate or this may also be accomplished by unequal spacing. ln this way, :l inueh greater eilieiency in the use spring is obtained tain a greater load. but a new complication is 'introduced in that the long plate or master leaf becomes stressed more highly than the shorter plates and is, therefore, likely to break first with the attendant disadvantages set forth. ,l further explained in my said patent hou' l overcame this disadvantage b v the inverse grading of the spring, thus reducing the thickness of the master leaf and decreasing the stress intensity therein. ln this way, l ani enabled to make use of very flexible tapers to obtain the highest eliieieney and the greatest final reaction, while still producing a structure in which the stress intensity was greatest in the shortest plat-es, which would, therefore., fail first` thus giving warningr and preventing 'total failure of the spring. The spring described in my said patent having they long and overlapping tapers and the inverse grading with' the thin master leaf and the other features of construction inferred to is the most efficient and most desirable spring that can be produced where the spring is called upon to act only as a spring and to withstand ere elusively or chiefly up and down loads causing the ordinary stresses to which a spring is supposed to be subjected.

As l haw set l'orth at the beginning ol' this slieeilication. however` there are some circurnstames in which a lspring is called upon to do other work in addition to that of taking up vertical shocks.l such, for instance, as acting as a strut for the transn'iission of drivingr power to a motor*propelled vehicle and also to various torsional stresses. ndereoiulitions such as theseH it is usually essential that the master leaf be made of heavy section and that the spring-lie of the form commonly known as a graded spring in which the leaves decrease vin thickness from the master leaf to the short plate, The. present invention teaches how such a graded spring having a relatively thick inaster leaf may he constructed in such a way that the master leaf will not fail first and at the same finie in which the material cone posing the spring shall be stressed in the most uniform manner other results sought and in Which the elliciency in the u c of the material shall be the of the material of theI and it is enabled to sus-A result in the master leaf failing compatible of ther highest obtainable under the conditions of use* These results are accomplished as follows:

lt being borne in mind that increasing the llexibility of the shorter plates increases the final reaction on the master leaf and thereby the eliiciency of the Spring, but that this process cannot be carried too far or the master leaf will break first, and it being further borne in mind that in the construction contemplated by the present application, the particular conditions of use to 'which the spring is to be put prevents the employment of a thinner master leaf as set forth in iny prior patent, it will at once appear that the reactions must be kept below that point which will stress the master leaf more than the other leaves and so first. Accordingly l take steps to so control the reactions as to increase them to the highest possible degree without causing the failure lirsl of the master leaf. As above stated, if the leaves` are of uniform thickness and the taper of each leaf is such as to make the flexibility7 of the stepped length thereof equal to the flexibility of a cantaliver beam of uniform strength then the reactions would be equal but nevertheless in the practical use of such spring, the master leaf would be likely to fail first owing to the stress reversals to which it is subected and which are p 'odueed by the nip and load stresses. The liability of the master leaf to break first is also increased if it is made thicker than the other leaves as the extreme liber stress therein is thereby increased. Consequently, l. make the tapers of the leaves of my spring and the lengths of overhang such that the flexibility of their stepped lengths gradually decreases from the short to the long plates, this flexibility preferably being for the short plates greater than` for the longer plates equal to and for the longest plates less than that of a canlaliver beam of uniform strength. The gradual decrease in the flexibility of the tapered part of the leaves from the short plate to the long plate or one below the master leaf. results in the support for the master leaf being gradually increased and the stress intensity therein reduced so that instead of failing first, it will become the last leaf to fail.

Referring to the drawings, it will be seen that the short leaf has the longest and most flexible taper, the llexibility of the stepped length or overhanging portion of this leaf, that is, the portion on each side of the perch or support, being somewhat greater than or if preferred substantially equal to the flexibility of a cantaliver beam of uniform strength `of a corresponding length. As has been described, the tapers of the subsequent leaves are successively decreased and also the stepped len ths or overhangs so that the liexibility` o these leaves, taken as a whole, and including their tapered ends and the stress rectifying slots is such that the entire lamina gradually decreases in dexibility as compared to one having the same width, length and thickness, but which is so tapered in the step as'to be in this distance the step) a beam of uniform strength. This decrease of flexibility in the proportion mentioned above reduces the load stress in the master leaf While it subjects the supporting plates to stresses consistent with a high and eicient stress distribution among them a'nd yet is such that the master leaf willnot fail first.

I also preferably .make use of stressrectifying slots such as 13, or 'other equivalent constructions, suchas illustrated, in Figs. 7 to 10, inclusive, these slots having the action described in my previous patent and serving to correct the stresses in the individual plates, so as to produce greater uniformity vof stress distribution and utilize the material effectively. These slots are preferably graduated in size, being largest in the shorter plates and decreasing to an extent in the longer plates in keeping with the conditions I have named, -that is the graduated increase of rigidity in the plates toward the master leaf so as to give the latter the maximum degree of support and prevent it from being excessively stressed.

'I have also introduced another feature of construction having the same general end in view, namely, the reduction of the stresses in the master leaf so as to enable it to better withstand the special stresses to which it is subjected in driving, torsional effects and reversal stresses due to rebound. This feature consists in the reduction of the nip stresses in the master leaf.

In springs as heretofore constructed, it has been customary to give each leaf. of the spring, including the long plateliv a more pronounced cixrvaiure than. the leaf immediatel y above it, so that when the leaves were hound together at the center and reduced to the new curvatures, each leaf would bear against the leaf above it with suliicient pressure to revent a separation between the ends of the leaves and the resulting gaping and chattering. The result of this binding, however, of the previously variously curved leaves was -to produce different internal stress conditions in the several leaves,thus the shorter and more curved leaves were straightened out, while the longer and less curved leaves were curved more. The resulting `stress condition, it will be seen, was that in the shorter leaves, a positive stress was produced, that is, a stress in the same direction as that produced by the load placed on the spring, while in the longer leaves, and particularly in the master leaf, a negative.

Yfunction 'the narrower portion stress was produced, or a stress opposite to that produced by the load. Consequently, where the s ring, as a whole was subsequently su ciently compressed, reversal stresses were set up in the master leaf and to a lesser extent also in the longer plates. The effect produced by the binding together of these variously-curved leaves is commonly referred to as the nip and the stresses set up are referred to as nip stresses. In the case of the old form of spring, in which'all of the leaves below the master leaf were given curvatures greater than the master leaf and in which the steps were equal, the nip. stress produced in the master leaf reached considerable proportions, and therefore, when the reversal of stress took p1ace, due to the* compression of the spring the range of stress to which the master lea was subyected Was very considerable.

Referring now to the Fig. 3, it will be seen that the long plate in my spring has the same initial curvature as the master leaf; therefore, the bringing together of the long plate and master leaf does not result in any increase-in the nip stress in the master leaf, but on the contrar the long plate reinforces the master leaf and assists 1t in resisting the forces produced by binding the lower curved leaves to the up er leaves. Thus, While the nip effect and t e resultant advantages are retained, the nip stress in the master leaf is greatly reduced, and theei'ect of stress reversal and the range of stresses to which the master leaf is subjected is therefore also greatly reduced. In some cases, the curvature of more than one of the longer plates may be made the leaf so that the three or even more upper leaves will unite in reducing the nip stresses produced by the joint action of the lower curved leaves. The initial or nip stress in the master leaf being thus reduced, it will be evident that the master leaf is in a condition `to better withstand the stresses due to driving or other external stresses to which it may be subjected, and, thereby is enabled to perform its much more satisfactorily. The reduction of the nip stress in the master leaf reduces the nip stress in all the other plates and hence also improves the whole spring.

In Figs. 2 and 5 shown various modified leaf constructions by which the rectification of the-stresses in the leaves may be attained. In Fig. 2, the stress rectifying slots 13 are shown as oval,

of the slot being toward the center of the leaf and the slot being broadest toward the outer end where the greatest reduction in section modulus is required. In Fig. 5, a form of slot is shown which has a relatively broad angular portion 14 at the outer end and a narrow slot portion 15 extending toward the center of the leaf. In Figs. 7 and 8, I have shown av same as that of the master to 10, inclusive, I have construction in which depressions 1G are formed in one face of the leaf adjacent to the sides thereof, the removal of metal due to these depressions resultin in the desired reduction in the section mo( ulus inl this rc gion. Figs. 9 and 10 show a single depression 17 formed at the proper part of the leaf producing a similar result. Other construe tions resulting in the modification of the section modulus so as to produce the desired stress rectification may be employed. lVhere I have used the expression stress rectifying slot herein and particularly' in the appended claims, I intend the term slot to be understood as general to include depressions or other equivalent structures. In Figs. 11 and 12, I have shown a construction Avfoaintroducing lubricant between the .leaves,`vvhich will be fed to the stress recti'fying slots so as to lubricate the entire spring. As here illustrated, the long plate 7 is extended out beyond the eye 4 at the end of the master leaf and is upwardly curvedA as indicated at 20. A groove 21 is formed in the inner surface of this upwardly curved portion preferably .by depressing a rib in the metal. Lubricant may be introduced in the u per open end of this groove and will fin its way down through the same and between the long plate and the master leaf. The lubricant Will then work through the slots 13 in the plates and so lubricate the various surfaces between all of the plates. Obviously this construction may be employed With other springs than the type set forth in the present appli cation, such, for instance, as a nonraded laminated spring or the spring descri ed in my previous patent referred to. The same is true of the various forms of stress rectifyin slots and depressions illustrated herein. "Se, construction which I employ for the M W tion of the nip stresses in the mas ter leaf may also be utilized in connection with springs other than those of the character here described.

While I have shown and described in detail certain preferred embodiments of my invention, these are to be unde'fstood as merely illustrative of the principle thereof and I do not desire to limit myself to such constructions as my invention may be utilized in other folms of springs. intend to cover my invention broadly in Whatever form its principle may find embodiment.

Having thus, described my invention, I claim:

1. A laminated leaf spring having the end portions of certain of the leaves tapered, the tapers decreasing in flexibility from the shorter to the longer plates.

2. A laminated leaf spring in which the stepped lengths or overhangs of the leaves eneric and in I, therefore,

decrease in length from the shorter to the longer plates, the ends of certain of the leaves being tapered and the tapers decreasing in flexibility from the shorter to the longer plates.

3. A graded laminated leaf spring having the master leaf thicker than the short plates and in which the stepped lengths or overhangs of the leaves decrease from the shorter plates toward the longer plates.

4. A graded laminated leaf spring in 'which the master leaf is thicker than the short plates, the stepped lengths or overhangs of the leaves decreasing from the shorter plates toward the longer plates, the ends of certain of the leaves being tapered, the flexibility of the tapers decreasing from the shorter plates toward the longer plates.

5. A graded laminated leaf spring, in which the master leaf is thicker than the short plates, the flexural characteristics of the successive leaves being so proportioned that the reactions between the leaves increase 'from the short plate to the final reaction between the master leaf and the long plate, said final reaction being insufficient to cause the master leaf to break first.

6. A laminated leafV spring in which certain of the intermediate plates are provided with stress rectifyinr slots ends and the point of support, and within the distance covered by the adjacent shorter plate, Ysaid slots decreasing in size from the shorter to the longer plates.

7. A laminated leaf spring having plates of graduated flexibility, the'flexibility decreasing from the short toward the longer plates, the flexibility of the stepped lengths or overhangs of the shorter plates being greater than, of the longer plates being substantially equal to and of the longest plates being less than the flexibility of corresponding cantaliver beams of uniform strength.

8. A laminated leaf spring having plates of graduated thickness, the thickness increasing from the short toward the longer plates, the flexibility of the stepped lengths between their or overhangs of the short plates being the flexibility of these leaves taken as a whole master leaf and 'one or and including their tapered ends being such that the successive leaves from the shorter to the longer leaves radually decrease in flexibility as comparetf same width length and thickness but so tapered in the step as to be in this distance a cantaliver beam of uniform strength.

11. A graduated laminated leaf spring, in which the master leaf is thicker than the shorter plate and in which the stepped lengths or overhangs decrease in length from the shorter toward the longer plates, certain of the leaves ing provided with stress rectifying slots, the flexibility of these leaves taken as a whole and including their tapered ends and stress rectifying slots bein such that the successive leaves adually ecrease in flexibility from the s orter to the longer leaves as compared to leaves having the same Width, length, and thickness, but so tapered in the step as t0 be in this distance a cantaliver beam of uniform strength.

12. A laminated leaf Spring having certain of the leaves formed with different free curvatures so as to produce nip, the free curvatures of some of the longest leaves being the same so as to reduce the nip stresses in such leaves.

13. A laminated leaf spring in which certain of the plates are formed with different free curvatures so as to produce nip, the

more plates adjacent thereto being formed with the same free curvature, so as to reduce nip stresses in the master leaf and therefore in all the leaves.

14. A graded laminated leaf spring in which the master leaf is thicker than the shorter plates, certain of the shorter plates being given different free curvatures, so as to produce nip, the master leaf and one or more of the longer plates having the same free curvature so as to reduce the nip stresses in the master leaf.

l5. A graded laminated leaf springr having the master leaf thicker than the shorter plates, the stepped lengths or over-hangs of the plates decreasing from the shorter to the. longer plates. certain of the plates being tapered. the fiexibility of the tapers deereasing from the shorter to the longer plates, certain of the plates beingr also formed ,with different free eurvatures to produce nip, the master leaf and one or more of the longer plates being` formed with the same free to leaves having the' being tapered and becurvature so as to reduce the nip stresses in the master leaf.

16. A laminated leaf spring, including a master leaf having an eye at the end thereof, and a long plate curved up adjacent to said eye and having a lubricant groove formed in the inner face of said upwardly curved portion.

17. A laminated leaf spring,r comprising a master leaf having an eye at the end thereof and supporting leaves having lubricating openings therein, the long plate of said spring having its end upwardly curved adjacent to said eye and having a lubricant receiving groove formed in. the inner face of said upwardly curved portion.

18. A graded laminated leaf spring in which the master leaf is thicker than the short plates and in which certain of the leaves are given different free curvatures so as to produce nip, the iexural characteristics of the successive leaves being so proportioned that the reactions between the leaves increase from the short plate to the final reaction between the master leaf and the long plate and in which the tapers decrease in flexibility and in length from the shortest plate to the longest plate, so that the said final reaction is insufficient when taken in conjunction with thel nip reversal stresses to cause the master leaf to break rst.

1S). A graded laminated leaf spring in which certain of the plates are formed with ditterent free curvatures so as to roduce a nip, one or more of the plates a( jacent to the master leaf having a radius of free curvature. equal to that of the master leaf increased by half the thickness of the respective leaf or leaves so as to reduce the nip and reversal stresses in the master leaf.

20. A lan'iinated leaf spring having a master leaf and other long' leaves thicker than the shortest leaf and of which the shorter leaves are tapered in such a manner that the tlexibilities of the tapers of these short leaves are greater than, the tlexihilities of the tapers of intermediate leaves are substantially equal to, and the the remaining.;l leaves are less than the tlexibilities of leaves of equal dimensions which are tapered in the steps so as to be cantaliver beamsl of uniform strength in these steps.

DA Vl l) LA NDAU.

flexibilities of fio 

